Field of the Invention
The invention pertains to two-component solventless adhesive compositions for lamination applications and structures, such as laminations and flexible laminated packaging, including those comprising metal or ink decals, comprising and/or made with the two-component solventless adhesive composition. The two-component solventless adhesive composition is softer than conventional two-component solventless adhesive compositions but retains the beneficial properties of conventional adhesives. The adhesive composition described herein comprises relatively high molecular weight oligomers and has an elongation.
The Related Art
Flexible packaging structures were traditionally made with solvent-borne laminating adhesives. Over the past 20-30 years, new water-borne and two-component solventless adhesives have been developed and commercialized to replace solvent-borne adhesives due to the benefit of lower costs and a desire in the industry for more environmentally friendly adhesives. However, some applications today remain using solvent-borne adhesive technology because of the specific performance of that technology and the properties of the substrates being bonded. Thus, two-component solventless laminating adhesives are not useful for all structures and applications.
Problematic structures for two-component solventless adhesives include (1) reverse printed film (i.e., polyethylene terephthalate (“PET”)) to metalized film (i.e., PET) and (2) reverse printed PET film with water-base inks to secondary films. Presently these structures are typically made with either solvent-borne or water-borne laminating adhesives. Metalized film is generally a plastic film sheet having attached to the film a layer of metal, generally a thin metal layer. Metalized films are used in flexible laminated packaging materials where it is desired to reflect light from the contents of the packaging or for visual appearance of consumer packaging.
Typical structures of reverse printed PET laminated to the metal side of metalized PET with typical two-component solventless laminating adhesive results in low bonds with up to 100% metal failure from the metalized PET. Such failure result typically does not happen when using solvent-borne or water-borne laminating adhesives. When two-component solventless adhesive is applied with reverse printed PET with water-base inks, the water-base ink decals off of the PET at lower bond values.
Conventional two-component solventless adhesives comprise relatively lower molecular weight monomers and relatively lower molecular weight oligomers that typically act as reactive diluents. These low molecular weight reactive materials generally provide favorable characteristics and properties for many, but not all, laminating applications. Without wishing to be bound by any theory, the inventor believes that in specific applications, such as those discussed above involving reverse printed film to metalized film and reverse printed film, including reverse printed PET film, with water-base inks to secondary films, the relatively lower molecular weight monomers and relatively lower molecular weight oligomers contribute to the negative affects of decaling metal (demetallization) or ink from the film.
All parts and percentages set forth herein are on a weight-by-weight basis unless specified otherwise. The molecular weight referred to herein is the number average molecular weight (Mn) in grams/mole (“g/mole”).